Atmospheric pollution affects us all. It affects our health and our environment. It is our activities and actions, however, which are resulting in the continual pollution of the atmosphere. For example, road transport has emerged as one of the most important sources of air pollution, particularly in urbanised areas such as mega-cities. Although emissions from other sources, such as industrial and domestic have reduced in developed countries, they still make a significant contribution to the overall pollution burden of the atmosphere in many less developed regions.

It is not only the directly emitted pollutants that can be hazardous to our health and the environment. Pollutants can also react with each other in the presence of sunlight to produce harmful photochemical smog, which affects many cities around the world. Once released into the atmosphere, pollutants can be dispersed into buildings and along streets as well as affect whole city areas. As a result of meteorological processes air pollution can also be transported across continents and, depending on the particular chemical species, remain in the global atmosphere for long periods of time. Pollution emitted locally by cars, industrial chimneys or forest fires, therefore, can have an impact on regional and global scales. On the other hand, pollutants such as aerosols and carbon dioxide, which influence the global radiation balance of the atmosphere, can lead to changes in the natural climate of the world with direct impacts on urban and local scales.